Refrigeration systems typically include several components, such as an evaporator, a condenser, an accumulator, a compressor and an expansion valve. It is common to conduct refrigerant between these devices in copper tubing. Copper tubing is often used in refrigeration systems because it is compatible with conventional refrigerants and may be readily cut and brazed in the field. The ability to make reliable, fluid-tight connections by brazing in the field is important as it insures that the refrigerant will not escape from the system through small openings or flaws in the brazed connections.
In many instances, the devices in the refrigeration system are made of steel. Therefore, the copper tubes which carry the refrigerant must at some point be placed in connection to a steel body. This may be done using threaded connectors or other types of adapters, however, such approaches are more expensive than brazing.
Connecting copper tubing to a steel body by brazing has often proven difficult because copper has a greater coefficient of thermal expansion than steel. When copper and steel materials are heated during brazing, the copper will expand locally much more than the steel. Similarly, upon cooling, the copper will contract more than the steel, resulting in relative dimensional changes. These differences in the rates of expansion and contraction may result in cracks in the brazing material. If the brazing is done at a connection in a refrigeration system, such cracks may result in a refrigerant leak. This is significant not only because lost refrigerant may disable the system, but also because many refrigerants cause problems which damage the environment.
To facilitate the installation of refrigeration systems in the field, steel components may be equipped with a section of copper tubing already attached to the component. In this way, the component may be readily connected using copper- to copper brazed connections. The welding of copper tubing to a steel body has been previously done by extending a copper tube through a slightly larger hole in an outer wall of the steel body of the device. A pre-formed mass of brazing material is placed in close proximity to the intersection of the body and the tube, and the assembly passed through a brazing furnace. In the furnace, the brazing material melts and flows into the space between the outside of the tube and the hole. Upon cooling, the film of brazing material in the space solidifies resulting in the tube and steel body being welded together.
There are two common problems with this approach to attaching a copper tube to a steel component. First, because the hole in the steel body must be slightly larger than the outside of the tube, the tube cannot always be made to extend at a right angle to the body. This is particularly true if the welding is attempted with the tube extending in a horizontal position. This problem can be reduced if the welding is done with the tube in the vertical position, however this is often not feasible. Attempts at furnace brazing with the tube extending horizontally, may result in the tube extending from the body at a random angle. When the steel component is installed in the field, the refrigerant-carrying tube will have to be connected to the tube section attached to the body at this random angle. Otherwise, the tubing will have to be bent to make the connection. This increases the difficulty involved in installing the component in the field, or if the tubing is bent, risks damaging the fragile film of brazing material holding the tube and the body together.
A further problem with furnace brazing using the approach previously discussed, occurs when the hole in the steel body is too close in size to the outer diameter of the tube. While keeping the hole in the steel body and the tube in close tolerance helps to support the tube during brazing in a horizontal position, it causes another problem. There is little space between the outside of the tube and the inside of the hole to begin with, and heating during brazing causes the tube to expand more than the hole. This reduces the space through which brazing material may flow. As a result, little or no brazing material enters the critical area between the outside of the tube and the hole to form the weld. This results in weak or imperfect joint which may ultimately leak.
Thus, there exists a need for a brazed joint construction that may be used to attach a copper tube to a steel body in the horizontal position in a manner that insures that the tubing will be in a desired alignment, and which provides a reliable, fluid tight connection between the tube and the body.